The design of high-precision accelerometers presents a number of common problems and goals. First, the accelerometer design should be based upon easily manufacturable parts that can be batch processed for low cost. Second, the accelerometer should be designed for high stability. This can be achieved by selecting highly stable parent materials for the accelerometer components, and by eliminating assembly joints in the sensor wherever possible. Third, the accelerometer should be sensitive to acceleration along a single axis, and insensitive to all other forms and directions of acceleration. Finally, the design should provide damping and shock caging within a simple assembly that does not require manual adjustment.
Many of the goals described above can be achieved by fabricating the accelerometer such that many of the key components, including the proof mass, flexures, and force transducers, are chemically machined using photolithography from a monolithic crystalline substrate. Unfortunately, in the past, while such accelerometers have been low in cost, they have also been relatively low-precision devices. One prior monolithic accelerometer is illustrated in U.K. Patent Application No. 2,162,314. The transducer described therein includes a U-shaped proof mass connected to a support by a pair of flexures, and a dual vibrating beam force transducer connected between the proof mass and the support. This structure is fabricated from a single crystal of silicon. Various means are described for causing the beams to oscillate, and for detecting the frequency of oscillation of the beams.
The accelerometer structure described in U.K. Patent Application No. 2,162,314 has a number of problems that limit its practical utility. For example, the proposed structure does not provide effective means for damping and shock caging of the proof mass. In addition, no techniques are disclosed for overcoming the relatively high inherent nonlinearity of the proposed structure. Finally, since the device is fabricated from silicon, comparatively complex means are required for causing and sensing beam vibration.